1. Field of the Invention
This invention relates a method and apparatus for selectively removing target sections of sheet metal from a continuous coil of sheet metal and placing those sections in one or more separate continuous coils of target sheet metal. In particular, the method comprises a cutting laser beam for removing target sections from a continuous coil and a welding laser beam for connecting target sections on one or more separate continuous coils. Cutting and welding procedures take place on an apparatus which aligns both the sheet metal and the cutting and welding laser beams with respect to the sheet metal. The present invention also relates to an apparatus which achieves both cutting and welding of sheet metal drawn from a continuous band of sheet metal in a continuous operation.
2. Description of the Relevant Art
In an industrial setting such as the automotive industry, automotive bodies are often made from a continuous coil of sheet metal having even thickness throughout. Sheet metal drawn from a sheet metal coil is cut and welded at specific locations to define an automotive body. It is important that the sheet metal band drawn from the coil be of uniform thickness within a specific tolerance range. Thus, a need arises for producing sheet metal bands of uniform thickness to meet the quality standards typically found in commercial or industrial applications such as the automotive industry. However, a recurring problem exists in that sheet metal bands coming from the manufacturer do not have the required uniformity of thickness. Rather than rejecting the entire coil, a need arises for selectively removing target sections which have defects such as errant thicknesses while still maintaining a continuous coil. Typical cutting and welding devices cannot interrupt a coil at the defective target location and cut the defective section from the coil and then subsequently weld the coil ends back together again while always maintaining uniform thicknesses within the finished coil product, and especially at the weld regions.
Conventional devices and methods not only cannot selectively remove defective regions from a continuous coil and subsequently evenly and uniformly join the coil back together again, but also conventional welding techniques do not provide a uniform weld location in the finished sheet metal product. Welding techniques typically include flash-butt welding, roll welding, clinching and plasma welding. Flash-butt welding requires the ends of each sheet metal portion be butt-joined to each other and resistance welded in the butt seam. Roll welding includes using roll welding electrons within the seam. Clinching generally embosses or presses together the ends of the sheet metal after they have been slightly overlapped. Still further, plasma jet welding also requires a slight seam overlap and higher heat introduction into the welded seam. Currently, all of the above methods demonstrate an exaggeration or bulge within this seam region. The overlap caused by clinching or plasma jet welding places an exaggeration in thickness at the seam location inappropriate for high quality, close tolerance sheet metal thicknesses needed for many industrial applications such as the automotive industry. The seam exaggerations not only cause inappropriate thickness extremes within the finished, welded product, but also results in off-centered coils of uneven sheet metal thicknesses. Although butt-laser welding procedures show promise, such as those discussed in European Patent No. EP-OS O 151 848, the disclosure of which is incorporated herein by reference, conventional machines needed for successful butt-welding procedures are expensive and difficult to manufacture.
In order to achieve a successful, even butt weld, it is important that the ends of the joined sheet metal be in precise alignment with each other. Conventional machines cannot achieve the needed amount of alignment precision in order to make butt welding commercially successful. Furthermore, if the sheet metals used are relatively thin, the butting together of the ends of the thin sheet metal may cause the ends to slightly buckle thereby causing potential seam exaggeration problems. Therefore, not only is it important that the ends be precisely aligned with one another, but the ends must be brought together with enough precision so that when they butt they do not buckle. The butt seam must also be deep-drawable and be made with a high precision and permanent constant quality. The cutting and welding operations must also be adaptable to a wide variety of sheet metal thicknesses and compositions. While butt-welding appears to have many of the advantages necessary for achieving uniform weld thickness throughout the sheet metal coil, conventional devices cannot incorporate both cutting and butt welding in an apparatus capable of achieving the necessary precision and adaptability required for current industrial settings.